Semiconductor wafer (“wafer”) fabrication often includes exposing a wafer to a plasma to allow the reactive constituents of the plasma to modify the surface of the wafer. The plasma processing of wafers is generally performed in a chamber in which a reactant gas is exposed to radiofrequency (RF) power to be transformed into the plasma. Currently, plasma confinement within the chamber is lost at high reactant gas flow rates. It is believed that this loss of the plasma confinement is due to Paschen breakdown in regions between the plasma and the chamber.
Electrons introduced into a neutral gas will gain energy if there is an electric field permeating the neutral gas. However, these same electrons will also lose energy via collisions with neutral gas molecules. If the energy gain of the electrons is, on average, large enough to ionize the neutral gas, plasma breakdown will occur. In the Paschen model, the effect of collisions between the electrons and the neutral gas molecules is characterized by the product (P*d), where (P) is the neutral gas pressure and (d) is a characteristic scale length of the device (the distance between the higher potential region and ground). The Paschen model qualitatively explains many observed reactant gas flow rate threshold trends for unconfinement of the plasma. Therefore, plasma confinement efforts have traditionally focused on minimizing the product (P*d). However, minimization of the product (P*d) often requires substantial re-design of existing plasma processing systems. Therefore, alternative methods are sought for improving plasma confinement while minimizing plasma processing system re-design.